1. Field of the Invention
The present invention relates to a linear motion guide unit composed of a sliding element straddling and movable along a track rail in a sliding manner.
2. Description of the Prior Art
Conventionally linear motion guide units shown in FIGS. 13 to 22 are well known to those skilled in the art.
Most prior linear motion guide units, as shown in FIGS. 13 to 22, each comprises a track rail 2 having opposing lengthwise side surfaces 3 on which are formed raceway grooves 4, and a sliding element, or slider 30, saddling the track rail 2 so as to freely move along and with respect to the track rail through rolling elements 5. The slider 30 is composed of a casing 9 formed with raceway grooves 8 confronting the raceway grooves 4 of the track rail 2, rolling elements, or rollers 5, running through raceways defined between the confronting raceway grooves 4, 8 so as to permit the slider to move relatively to the track rail, end caps 31 arranged on the end surfaces opposing in the moving direction of the casing 9 or lengthwise, one to each end surface, end seals 32 secured on the end caps 31 so as to close clearances between the track rail 2 and the end caps 31, and bottom seals 11 arranged on the lower surfaces of the casing 9 and the end caps 31 so as to close clearances between the track rail 2 and both the casing 9 and end caps 31. The casing 9 is further formed with threaded openings 34 for attaching thereto a table and other appliances, parts or the like by screws.
The slider 30 is movable in a straddling attitude along the track rail 2 through rolling elements 5, which may run in a circulating manner through the raceways defined between the raceway grooves 4, 8, turnarounds 14 (refer to FIG. 21) in the end caps 31 and return passages 13 bored in the casing 9. Provided on the end surfaces of the end seals 32 and the side surfaces of the end caps 31 are grease nipples 35 for supplying lubricant to the sliding interfaces between the raceways and the rolling elements 5.
The end seals 32 are each comprised of a core plate 21 of metals such as steal or the like, an elastic sealing member 22 of synthetic rubbers, synthetic resins or the like secured to the core plate 21. Upon having mounting any end seal 32 on its associated end cap 31, a lip 24 of the sealing member 22 may make tight contact with the lengthwise side surfaces of the truck rail 2 so as to close the clearances between the track rail 2 and the end caps 31.
Screws are available for mounting the end seals 32 onto the end caps 31. The end seals 32 have been usually secured on the end surfaces of the casing 9 through the screws 36 together with the end caps 31. As an alternative, following screwing the end caps 31 on the end surfaces of the casing 9, the end seals 32 have been secured on the end caps 31 with the other screws.
On the prior linear motion guide unit having the end seals 32 screwed on the casing 9, attachment and/or detachment of the bottom seals has been troublesome in need of repair and replacement of the end seals. Moreover, the screws are often limited in their permissible locations so that, in some cases, it is hard to help ensure the reliable fixing of the seal ends. This has caused a major problem of deterioration in sealing performance. In case of screwing the end seals 32 on the ends of the casing 9 together with the end caps 31, the positioning error is liable to happen in matching of the end seals 32 with the track rail 2 and end caps 31 owing to the scattering in boring precision of the fitting openings 28, 39 of the end caps 31 and end seals 32. In contrast, on an alternative where the end seals 32, after having screwed the end caps 31 on the ends of the casing 9, are secured on the end caps 31 with the other screws, extra spaces for boring additional openings in the end caps 31 are required and, therefore, adverse the recently increasing requirement for miniaturization of the linear motion guide units.
There have been also known the mounting structures of the end seals onto the slider, in which the end seals are mounted to the bottom seals with the engagement with the latter. Disclosed in Japanese Utility Model Laid-Open Nos. 51547/1994 and 51548/1994 are examples of the mounting structure of the end seals to the bottom seals, in which the end seal has protrusions while the bottom seal has the complementary recesses whereby the engagement of the protrusions with the recesses results in securing the end seal to the bottom seal.
The slider has been alternatively known wherein the end seals are mounted in a snapping manner on a frame body of hollow rectangular in section, which is composed of end plates and side plates and incorporated with the casing and end caps. In the prior art, the end seal is produced by the injection molding of synthetic resins or synthetic rubbers and comprised of platy members abutted against the frame body, sealing members making contact with the track rail, and snap fasteners extending outwardly from the back sides of the platy members. On the other hand, the frame body is formed with perforations in its end plates while the end caps have openings in alignment with the perforations. The end seals may be thus secured to the casing with the fitting engagement of the snap fasteners into the perforations of the frame body and the openings in the end caps. Japanese Patent Laid-Open No. 264322/1997 discloses an example of the prior art described just above.
Nevertheless, the prior slider of the type in which end caps, casing and end seals are all incorporated in the frame body becomes inevitably complicated and large-sized in structure and therefore does no deal with the recent need of miniaturization. That is to say, as the end seal integral with the snap fasteners has required a greater strength on snap-fitting the fasteners into the perforations and the openings, the end seal has to be rendered larger in thickness, resulting in making the slider longer and thus disadvantageous to the miniaturization of the motion guide units.